Millimeter-sized spherical ion-sieve foams with hierarchical pore structure for recovery of lithium from seawater

Millimeter-sized spherical ion-sieve foams (SIFs) were prepared from spinel lithium manganese oxide (LMO) via a combined process of foaming, drop-in-oil, and agar gelation to recover the lithium from natural seawater. The spinel structure of the fabricated SIFs was induced by H+–Li+ ion exchange after acid treatment, and the SIFs were found to exhibit hierarchical trimodal pore structure. Small and large bimodal mesopores were formed from the acid treatment-induced agar removal, and macropores from the bubble-template. Increasing agar content during the fabrication process led to an increase in the specific surface area and mesopore volume of the SIFs, but a decrease in the macropore volume. The amount of lithium adsorption in the LiOH solution was significantly decreased with increasing agar content during the fabrication process, probably because the SIFs fabricated with lower agar content possessed more open pores, which in turn increased the contact probability with the hierarchical structure developed in the inner parts of the SIFs. The SIFs with the lowest agar content exhibited greatest lithium adsorption capacity in natural seawater of 3.4 mg g−1, and the adsorption and desorption efficiency were almost unaffected even after five adsorption–desorption cycles.

► Millimeter-sized spherical ion-sieve foams (SIFs) are prepared for Li+ recovery.
► SIFs exhibit spinel structure and hierarchical trimodal pore structure.
► Li+ adsorption of SIFs in LiOH solution decreases with agar content.
► Li+ adsorption efficiency is over 95% even after five adsorption–desorption cycles.
► Li+ desorption efficiency is maintained at about 86% after five treatment cycles.